1. Work, Power and Machines
Chapter 14
Work, Power and Machines

2. Chapter 14.1 F d

3. Work
Work Requires Motion 
The force must act in the same direction that the object moves.
If there is no movement, no work is done.

4. Work depends on direction!!

5. Work depends on direction!!
No Work!!

6. Work depends on direction!!

7. Work = Force X distance W = F X d W = Newton X meter = N·m
W = Joule (J)

8. Fd
W = W
W d
F = F d
W F
d =

9. Power
Work
Time
Power =
P = t W

10. Pt
W = W
W t
P = P t
W P
t =

11. Increase work done in same time. Same amount of work in less time.
Increase Power
Increase work done in same time.
Same amount of work in less time.

12. Power
Joules
seconds
= Watts
Power = s J
P =
= W

13. Example
You exert a vertical force of 72 N to lift a box to a height of 1.0 m in a time of 2.0 s. How much power is used to lift the box?

14. P = 36 J/s = 36 W Given: F =72 N d=1.0 m t = 2.0s Find: P =?
Equation: P = W/t w = Fd P = Fd/t
Solve: P = (72N x 1.0m)/2.0s
P = 36 J/s = 36 W

15. James Watt - Horsepower
1 horsepower is equal to 746 watts

16. Homework
Worksheet: 14-1
Due: 4/5/10

17. Chapter 14.2 Work = Force X distance Machines
Can machines decrease work???
Work = Force X distance

18. Machines do Work

19. Machines do Work Work = Force X distance
Machines make work easier to do.
Work =
Force X
distance
Change the size of a force needed
The direction of a force.
The distance over which a force acts.

20. Increasing Force

21. Direction of Force

22. Distance the force acts.

23. Work Input and Work Output

24. Work Input and Work Output

25. Work Input and Work Output
Because of friction, the work done by a machine (output work) is always less than the work done on the machine (input work).

26. Work Input to a machine
The force you exert on a machine is called the input force.
The distance the input force acts through is known as the input distance

27. Work Input to a machine

28. Work Output from a machine
The force exerted by a machine is called the output force.
The distance the output force acts through is known as the output distance.

29. Work Output from a machine

30. Homework
Worksheet: 14-1
Worksheet: 14-2
Due: 4/5/10

31. Chapter: 14-3
Mechanical Advantage
And
Efficiency

32. Actual Mechanical Advantage
Actual Mechanical Advantage (MA)
The number of times a machine multiplies the Input Force.

33. Actual Mechanical AdvantageFI FO

34. Input Force - FI
Output Force - FO

35. Actual Mechanical Advantage
MA = Output Force
Input force
MA = FO FI

36. Experiment

38. Ideal Mechanical Advantage
(IMA)
IMA of a machine is the mechanical advantage in the
absence of friction.

39. Ideal Mechanical AdvantageDI Do

40. Ideal Mechanical Advantage - IMA
IMA = Input Distance
Output Distance
MA = DI DO

41. Experiment

43. MA Example
Example: Mr. Clune is trying to move a large stone in his yard. He uses a crow bar that gives him a Mechanical Advantage of 100. If the stone weighs 1000N,
what force must Mr. Clune apply
to move it?

44. Fe = 10N Find: Fe = ? Equation: Fe = Fr MA Solve: Fe = 1000N 100
Given: MA = Fr = 1000N
Find: Fe = ?
Equation: Fe = Fr MA
Solve: Fe = 1000N
100
Fe = 10N

45. Efficiency
The measure of how much work put into a machine is changed to useful work put out by the machine
Work
Input
(WIN)
Work
Output
(WOUT)

46. WOUT WIN
Efficiency = X 100%
Fo • Do FI • DI
Efficiency = X 100%

47. Experiment

49. Example: A sofa weighing
must be placed in a truck bed
off the ground.
A worker uses a force of
to push the sofa up an inclined plane that has a slope length of What is the of the inclined plane?
1500N
1.0m
500N
4.0m.
efficiency

50. Fo = 1500N
FI = 500N
l = 4m
(DI)
h = 1m (Do)

51. Efficiency = 75% Given: Fo = 1500N Do = 1.0m FI = 500N DI = 4.0m
Find: Efficiency = ?
FI • DI Fo • Do
Equation: Efficiency = X100%
Solve: Eff. = X100%
1500N•1.0m 500N•4.0m
Efficiency = 75%

52. Worksheet: 14-3 Math Practice: Page: 425 1-3 Page: 426 8-9 Due: 4/7/10
Homework
Worksheet: 14-3
Math Practice:
Page:
Page:
Due: 4/7/10

53. A student working in a grocery store after school pushes several grocery carts together along a ramp. The ramp is 3 meters long and rises 0.5 meter. What is the ideal mechanical advantage of the ramp?

54. A construction worker moves a crowbar through a distance of 0
A construction worker moves a crowbar through a distance of 0.50 m to lift a load 0.05 m off of the ground. What is the IMA of the crowbar?

55. The IMA of a simple machine is 2.5. If the
output distance of the machine is 1.0 m,
what is the input distance?

56. You have just designed a machine that uses 1000 J
of work from a motor for every 800 J of
useful work the machine supplies.
What is the efficiency of your machine?      

57. If a machine has an efficiency of 40%,
and you do 1000 J of work on the machine,
what will be the work output of the machine?

58. Lever

59. Wheel and Axle

60. Pulley

61. Inclined Plane

62. Screw

63. Wedge

64. Work
Work In = Work Out
Work = Force · Distance

65. FI Do DI Fo

66. Wout = Win
Fo x Do = FI x DI

67. Example: If the stone has to be moved to 0. 1m high, how far does Mr
Example: If the stone has to be moved to 0.1m high, how far does Mr. Clune have to apply his force.
Given: Fo = 1000N Find: de = ?
dr = 0.1m
Fe = 10N
Equation: de = ( Fr x dr ) / Fe
= ( 1000N x 0.1m ) / 10N
de = 10m

68. Ideal Mechanical Advantage IMA
Ideal Machine – A machine in which the work input equals work output.
Win = Wout

69. A bar that is free to pivot
The Lever
A bar that is free to pivot
about a fixed point.. Fi Fo Di Do
Fulcrum..

70. Do IMA for the Lever IMAlever = input arm length output arm length
IMAlever = Di Do

71. Given: Do = 0.50cm Find: IMA Di = 20cm Equation: MA = Di Do
Example: A screwdriver is used to pry open the lid of a paint can. The output arm is 0.50cm long. The input arm is 20cm long. What is the mechanical advantage of the screwdriver?
Given: Do = 0.50cm Find: IMA
Di = 20cm
Equation: MA = Di Do
Solve: IMA = 20 cm cm
IMA = 40

72. Classes of Levers
First Class O I O I
Second Class O I
Third Class

73. Wheel and Axle
A wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together.

75. Wheel and Axle

76. No Power Steering!!

77. Wheel and Axle ra rw

78. rw ra IMAWheel&Axle= rw ra IMA of a Wheel and Axle
IMA = radius of wheel
radius of axle rw ra rw ra
IMAWheel&Axle=

79. Solve: IMA = 20cm 2cm IMA = 10 Given: rw = 20cm Find: IMA = ? ra = 2cm
Example: An antique car, with no power steering, has a steering wheel with a radius of 20cm. The wheel turns an axle that has a radius of 2cm. What is the Mechanical Advantage of this wheel and axle system?
Given: rw = 20cm Find: IMA = ?
ra = 2cm
Equation: IMA = rw ra
Solve: IMA = 20cm
2cm
IMA = 10

80. A slanted surface used to raise objects
Inclined Plane
A slanted surface used to raise objects

81. IMA of an Inclined Planeh l h
IMA Inclined Plane =

82. Example: A piano must be raised from the ground to the first floor, a distance of 0.5m. A 10m plank is used to help to movers pick the piano up. If the piano weighs 3000N, what force do the movers have to apply to the piano?

83. l = 10m
Fo = 3000N
h = .5m

84. Find: IMA = ? Fi = ? Given: length ( l ) = 10m height ( h ) = 0.5m
Fo = 3000N
Find: IMA = ?
Fi = ?

85. Equation: IMA = l h Solve IMA = 10m 0.5m IMA = 20 Equation: Fi = Fo MA
Solve Fi = 3000N 20
Fi = 150N

86. An inclined plane with either one or two sloping sides.
Wedge
An inclined plane with either one or two sloping sides.
More
IMA

87. IMAScrew – Number of Threads
An inclined plane wound around a cylinder.
More
IMA
IMAScrew – Number of Threads

88. Pulleys
Fixed
Pulley
Movable
Pulley

89. Fixed Pulleys

90. Fixed Pulleys
Fixed
Pulley I O I
1st Class Lever O

91. Movable Pulleys

92. Movable Pulleys R E
2nd Class Lever I
Movable
Pulley O

93. Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight.
30N
30N
30N
IMA = 1

94. Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight.
15N
15N
15N
30N
IMA = 2

95. Ideal Mechanical Advantage of a Pulley: The number of ropes segments supporting the resistance weight.
10N
10N
10N
10N
30N
IMA = 3

96. The arrangement of several pulleys.
Block and Tackle
The arrangement of several pulleys.

97. A machine made by combining two or more simple machines together.
Compound Machine
A machine made by combining two
or more simple machines together. Yo

100. Packet 14-4 Word Wise & Math Due: 4/13/10
Homework 14-4
Packet 14-4 Word Wise & Math Due: 4/13/10
Test: 4/15/10

101. The science of designing artificial replacements for parts
Mending with Machines
Bionics
The science of designing artificial
replacements for parts
of the human body

102. Artificial replacements for human limbs.
Prostheses
Artificial replacements for human limbs.

103. Functional Neuromuscular Stimulation FNS
Brain
Touch
Sensors
Receiver
Transmitter

104. Homework 7-4
Section Wrap-Up Page: 197
Due 01/7/05

105. Power is the rate at which
work is done.
Power =
work time
P =
F • d t

106. Example : A figure skater lifts his partner, who weighs 450N, 1
Example : A figure skater lifts his partner, who weighs 450N, 1.0m in 3.0s. How much power is required.
d = 1m
t = 3s

107. P = 150W Given: F = 450N d = 1.0m t = 3.0s Find: Power F • d t
Equation: P =
F • d t
450N • 1.0m s
Solve: P =
P = 150W